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Throw error when assigning jsonb scalar instead of a composite object

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During the jsonb subscripting assignment, the provided path might assume an
object or an array where the source jsonb has a scalar value.  Initial
subscripting assignment logic will skip such an update operation with no
message shown.  This commit makes it throw an error to indicate this type
of situation.

Discussion: https://postgr.es/m/CA%2Bq6zcV8qvGcDXurwwgUbwACV86Th7G80pnubg42e-p9gsSf%3Dg%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2Bq6zcX3mdxGCgdThzuySwH-ApyHHM-G4oB1R0fn0j2hZqqkLQ%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2Bq6zcVDuGBv%3DM0FqBYX8DPebS3F_0KQ6OVFobGJPM507_SZ_w%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2Bq6zcVovR%2BXY4mfk-7oNk-rF91gH0PebnNfuUjuuDsyHjOcVA%40mail.gmail.com
Author: Dmitry Dolgov
Reviewed-by: Tom Lane, Arthur Zakirov, Pavel Stehule, Dian M Fay
Reviewed-by: Andrew Dunstan, Chapman Flack, Merlin Moncure, Peter Geoghegan
Reviewed-by: Alvaro Herrera, Jim Nasby, Josh Berkus, Victor Wagner
Reviewed-by: Aleksander Alekseev, Robert Haas, Oleg Bartunov
This commit is contained in:
Alexander Korotkov
2021-01-31 23:51:06 +03:00
parent 81fcc72e66
commit aa6e46daf5
4 changed files with 104 additions and 8 deletions
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39
doc/src/sgml/json.sgml
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@ -614,8 +614,24 @@ SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @> '{"tags": ["qu
The result of a subscripting expression is always of the jsonb data type.
</para>
<para>
<command>UPDATE</command> statements may use subscripting in the
<literal>SET</literal> clause to modify <type>jsonb</type> values. Subscript
paths must be traversible for all affected values insofar as they exist. For
instance, the path <literal>val['a']['b']['c']</literal> can be traversed all
the way to <literal>c</literal> if every <literal>val</literal>,
<literal>val['a']</literal>, and <literal>val['a']['b']</literal> is an
object. If any <literal>val['a']</literal> or <literal>val['a']['b']</literal>
is not defined, it will be created as an empty object and filled as
necessary. However, if any <literal>val</literal> itself or one of the
intermediary values is defined as a non-object such as a string, number, or
<literal>jsonb</literal> <literal>null</literal>, traversal cannot proceed so
an error is raised and the transaction aborted.
</para>
<para>
An example of subscripting syntax:
<programlisting>
-- Extract object value by key
@ -631,6 +647,10 @@ SELECT ('[1, "2", null]'::jsonb)[1];
-- value must be of the jsonb type as well
UPDATE table_name SET jsonb_field['key'] = '1';
-- This will raise an error if any record's jsonb_field['a']['b'] is something
-- other than an object. For example, the value {"a": 1} has no 'b' key.
UPDATE table_name SET jsonb_field['a']['b']['c'] = '1';
-- Filter records using a WHERE clause with subscripting. Since the result of
-- subscripting is jsonb, the value we compare it against must also be jsonb.
-- The double quotes make "value" also a valid jsonb string.
@ -639,8 +659,9 @@ SELECT * FROM table_name WHERE jsonb_field['key'] = '"value"';
<type>jsonb</type> assignment via subscripting handles a few edge cases
differently from <literal>jsonb_set</literal>. When a source <type>jsonb</type>
is <literal>NULL</literal>, assignment via subscripting will proceed as if
it was an empty JSON object:
value is <literal>NULL</literal>, assignment via subscripting will proceed
as if it was an empty JSON value of the type (object or array) implied by the
subscript key:
<programlisting>
-- Where jsonb_field was NULL, it is now {"a": 1}
@ -661,17 +682,19 @@ UPDATE table_name SET jsonb_field[2] = '2';
</programlisting>
A <type>jsonb</type> value will accept assignments to nonexistent subscript
paths as long as the last existing path key is an object or an array. Since
the final subscript is not traversed, it may be an object key. Nested arrays
will be created and <literal>NULL</literal>-padded according to the path until
the value can be placed appropriately.
paths as long as the last existing element to be traversed is an object or
array, as implied by the corresponding subscript (the element indicated by
the last subscript in the path is not traversed and may be anything). Nested
array and object structures will be created, and in the former case
<literal>null</literal>-padded, as specified by the subscript path until the
assigned value can be placed.
<programlisting>
-- Where jsonb_field was {}, it is now {'a': [{'b': 1}]}
UPDATE table_name SET jsonb_field['a'][0]['b'] = '1';
-- Where jsonb_field was [], it is now [{'a': 1}]
UPDATE table_name SET jsonb_field[0]['a'] = '1';
-- Where jsonb_field was [], it is now [null, {'a': 1}]
UPDATE table_name SET jsonb_field[1]['a'] = '1';
</programlisting>
</para>